Former First Daughter Caroline Kennedy and her fellow jurors took just over an hour today to acquit a Harlem man of charges that he sold four “nickel bag” crack rocks at $5 each to an undercover officer near Harlem River Park.

Violent predicate felon Nelson Chatman, 31, smiled big as the jury foreman rendered the not guilty verdict in the circumstantial case after just 75 minutes of deliberations.

And Kennedy, 55, also smiled, slightly and politely, as the jurors were individually asked by a clerk, “Is that your verdict?”

“Yes,” Kennedy said when it was her turn, nodding. The lawyer and philanthropist had sallied amiably through jury duty since her selection as Juror No. 7 a week ago, enjoying lunches and hallway chats with her fellow panelists during down town.

She left the courthouse looking blue jeans-chic in good boots and a Prada satchel, declining to talk to reporters and still chatting with her fellow jurors.

The good news for Chatman, a veteran drug dealer and thief, is that he has now dodged a mandatory minimum prison sentence of six years on the single charge against him, felony criminal sale of a controlled substance.

But the bad news was that he could not be immediately released due to an outstanding Department of Correction matter.

His court-appointed lawyer, Mark Jankowitz, had insisted in closing arguments that Chatman was the wrong guy, and had gotten swept up in a crack buy-and-bust operation in an instance of mistaken identity.

Cops never saw Chatman hand drugs to an alleged steerer, and he had no drugs or pre-recorded buy money on him when he was apprehended after a lengthy chase, the lawyer had argued.

Instead, police witnesses told jurors that they assumed the hand-to-hand contact between a “steerer” and a man who looked like Chatman was a drug hand-off.

And Chatman could have dropped contraband along the FDR Drive or near a highway overpass as he fled on foot from police, prosecutors had argued.

“A criminal case is not about assumptions, guess work and speculations,” the lawyer told jurors in closings this morning.

“The jury has made the right decision and we’re glad that the right thing ws done,” Jankowitz said after the verdict.

Jankowitz had taken a chance on choosing Kennedy small-time drug bust despite her having had close ties to Manhattan DA Cyrus Vance. Kennedy has known Vance since elementary school and had headlined at fundraisers during his campaign.

Chatman has served at least six years prison on prior drug sales and attempted robbery convictions.